Replace IndexablePath with ResourceUri concept

[vinistock]

Motivation

I spend some time thinking in more detail about #2341. At the core of the issue, I think we're missing our own URI abstraction.

And indexable path is currently the same thing as a file URI, with the extra attribute of require path. If we introduce a Uri concept to the indexer, we can standardize the entire language server and index on it, which will make it more consistent and allow #2341 to move forward in a better way.

In fact, I think we may not even need to store locations in entries anymore, since we only use those to construct URIs, but that can be encoded as the URI's fragment, which I believe may also simplify #2051.

This change has no impact in indexing time or memory used.

Implementation

Created a RubyIndexer::Uri object, which is essentially just URI::Generic with our extra bits of behaviour. The next steps is to continue standardizing on RubyIndexer::Uri and get rid of other cases of URI::Generic.

Automated Tests

Adapted existing tests.

[st0012]

I still prefer a clearer class name than Uri given its origin is the indexer and not just the language server. But we can worry about it later as well.

[st0012]

BTW, I think this counts as a breaking change as addon tests can use index_single, which now requires a different type.

[st0012]

BTW, are we still going to need lib/core_ext/uri.rb after this?

[vinistock]

BTW, are we still going to need lib/core_ext/uri.rb after this?

We'll get rid of that on the follow up to this PR, where we should start using the new Uri class everywhere.